The present invention relates to a thermoplastic polyimide, and an aromatic diamine compound used in the production of the polyimide.
The thermoplastic polyimide of the present invention has at least excellent characteristics {circle around (1)} to {circle around (4)} described below.
{circle around (1)} It is superior in thermal stability on melting. That is, the degree of lowering of the fluidity on melting with a lapse of time is small. It was difficult to realize this feature in the prior art.
{circle around (2)} It has high heat resistance. That is, it has excellent mechanical strength even at the temperature higher than a glass transition temperature (Tg) because of its high crystallizability.
{circle around (3)} It is superior in productivity. That is, since a crystallization rate is large, it is crystallized during a normal short molding cycle without requiring a special heat-treating operation such as operation of slowly cooling in a mold on molding, operation of heat-treating after molding or the like.
{circle around (4)} It is superior in dimensional accuracy. That is, since a crystallization rate is large and it is crystallized in a mold on molding, the degree of shrinkage after molding is small.
The aromatic diamine compound of the present invention has at least excellent characteristics {circle around (5)} to {circle around (6)} described below.
{circle around (5)} The content of an azo compound is very small.
{circle around (6)} A polyimide resin having excellent thermal stability on melting can be obtained.
a) Filed of the Invention
{circle around (1)} Characteristics and application of polyimide
Polyimide has widely been used in the fields of molding materials, composite materials, electric/electronic parts, etc. because of its excellent characteristics such as mechanical properties, chemical resistance, flame retardance, electric characteristics, etc., including excellent heat resistance.
{circle around (2)} xe2x80x9cVespelxe2x80x9d (manufactured by Du Pont Co.) and xe2x80x9cUpimolxe2x80x9d (manufactured by Ube Industries, Ltd.)
As the polyimide for molding material and composite material, xe2x80x9cVespelxe2x80x9d (trade name, manufactured by Du Pont Co.) and xe2x80x9cUpimolxe2x80x9d (trade name, manufactured by Ube Industries, Ltd.) are known, but both polyimides were inferior in moldability because they are insoluble and infusible. That is, to obtain a molded article of the polyimide, it was necessary to mold from polyamic acid as a polyimide precursor by using a special means such as sintering. The problem is that it is difficult to obtain a product having a complicated shape by sintering. To obtain the product having a complicated shape, a desired shape must be skived from a block by using a cutting machine such as NC lathe and the like. Therefore, there was a problem about the cost required to complicated machining and forming steps.
{circle around (3)} xe2x80x9cUltemxe2x80x9d (manufactured by General Electric Co.)
As an injection-moldable thermoplastic polyimide having improved moldability, for example, xe2x80x9cUltemxe2x80x9d (trade name, manufactured by General Electric Co.) is known (U.S. Pat. Nos. 3,847,867 and 3,847,869).
However, since this polyimide is completely non-crystalline and has a glass transition temperature (Tg) of 215xc2x0 C., it has not sufficient heat resistance, necessarily, when assuming use at a high temperature range.
That is, when it is evaluated by a deflection temperature under load (DTUL) which indicates s substantial working limit of temperature, the temperature of neat xe2x80x9cUltemxe2x80x9d is 200xc2x0 C. and that of (CF30) xe2x80x9cUltemxe2x80x9d containing 30% by weight of carbon fibers is 212xc2x0 C. Therefore, when assuming use at a high temperature range, both of them are not a high numerical value as a super engineering plastic.
{circle around (4)} xe2x80x9cAURUMxe2x80x9d (manufactured by Mitsui Chemicals, Inc.)
As the injection-moldable thermoplastic polyimide having improved moldability, for example, xe2x80x9cAURUMxe2x80x9d (trade name, manufactured by Mitsui Chemicals, Inc.) was newly developed (Japanese Patent Laid-Open No. 62-68817).
This polyimide is superior in thermal stability on melting and is suitably applied to melt molding such as extrusion molding and injection molding. Regarding xe2x80x9cAURUMxe2x80x9d, a melt viscosity ratio MVR calculated by the numerical formula (1) is within a numerical range shown in the numerical formula 2.
The glass transition temperature (Tg) of this polyimide is 245xc2x0 C. and, when it is evaluated by the reflection temperature under load (DTUL), the temperature of neat xe2x80x9cAURUMxe2x80x9d is 238xc2x0 C. and that of (CF30) xe2x80x9cAURUMxe2x80x9d containing 30% by weight of carbon fibers is 248xc2x0 C. Therefore, xe2x80x9cAURUMxe2x80x9d is superior in heat resistance to xe2x80x9cUltemxe2x80x9d.
xe2x80x9cAURUMxe2x80x9d is essentially crystalline and can be crystallized by heat-treating (annealing treatment, annealing) after molding. Regarding DUTL of xe2x80x9cAURUMxe2x80x9d when it is crystallized, the temperature of neat xe2x80x9cAURUMxe2x80x9d is 260xc2x0 C. and that of (CF30) xe2x80x9cAURUMxe2x80x9d containing 30% by weight of carbon fibers is 349xc2x0 C. Therefore, xe2x80x9cAURUMxe2x80x9d has a markedly higher heat resistance than the case where it is not crystallized.
As described above, xe2x80x9cAURUMxe2x80x9d is crystalline and has high glass transition temperature and high melting point, and has highest heat resistance among thermoplastic resins. However, this polyimide is slowly crystallized, that is, it takes a long time to complete the crystallization is long. Furthermore, a molded article obtained by a general molding cycle, e.g. injection molding cycle of about 30 to 60 seconds, is amorphous.
Therefore, the molded article thus obtained has such a feature that it is superior in dimensional accuracy and flexural modulus as far as it is used at a temperature lower than the glass transition point.
On the other hand, when the molded article thus obtained is used under the conditions of a temperature higher than the glass transition point, the modulus is drastically lowered and the shape of the molded article can not be retained, thereby making it impossible to use it continuously.
When this molded article made of xe2x80x9cAURUMxe2x80x9d is continuously used under the conditions of a temperature higher than the glass transition point, the amorphous molded article may be crystallized by subjecting to a heat treatment. However, a heat-treating operation requiring a long time drastically lowers the productivity and, furthermore, shrinkage along with crystallization causes problems such as dimensional change, deformation, surface roughening and the like.
If the molded article obtained by molding xe2x80x9cAURUMxe2x80x9d is sufficiently crystallized without requiring a special heat treatment (e.g. slow cooling in mold, heat treatment after molding, etc.), these problems do not occur. Therefore, there has been developed a technique of accelerating the crystallization by adding to xe2x80x9cAURUMxe2x80x9d an organic low-molecular weight compound and a crystalline resin having low heat resistance (Japanese Patent Laid-Open Nos. 9-104756 and 9-188813).
However, these methods have such a problem that the heat and chemical resistances are lowered because the low-molecular weight compound and resin having low heat resistance are added.
{circle around (5)} Polyimide having a repeating unit represented by the chemical formula (1).
Polyimide having a repeating unit represented by the chemical formula (1) is disclosed in Japanese Patent Laid-Open Nos. 61-143433, 62-11727 and 63-172735, and crystallizability and fast crystallization are shown.
Accordingly, if this polyimide can be applied to injection molding and can be crystallized in a mold during a conventional molding cycle, it is assumed that the resulting molded article has high heat resistance and high dimensional accuracy.
However, since molecular terminal of the polyimide produced in accordance with such a disclosure is not deactivated, the thermal stability on melting is drastically low and the fluidity is lowered quickly within a short time. Therefore, it was not practical to apply the polyimide to melt molding such as extrusion molding, injection molding or the like.
{circle around (6)} Polyimide having a repeating unit represented by the chemical formula (1), molecular terminal of which is composed of the chemical formula (2) and/or chemical formula (3)
Macromolecules, Vol. 29, pages 135-142 (1996) and Macromolecules, Vol. 30, pages 1012-1022 (1997) disclose a technique of improving the thermal stability on melting of the polyimide by reacting the molecular terminal of the polyimide with an aromatic dicarboxylic anhydride to deactivate the molecular terminal. However, this disclosure shows that, even if the molecular terminal of the polyimide is deactivated, the melt viscosity increases by 1.65 times or higher as that of the initial viscosity on maintaining at 420xc2x0 C. for 30 minutes.
It is known that, when the resin whose melt viscosity increases with a lapse of time is injection-molded under fixed molding conditions, the fluidity of the resin is lowered with a lapse of time after the beginning of the molding to cause a problem that the resin does not reach all of the corners of the mold and physical properties of the resulting product are not constant. Therefore, it had not been performed to apply the polyimide to injection molding.
Actually, as shown in the Comparative Examples of the present invention, the polyimide produced in accordance with such a disclosure showed an increase in viscosity on melting and could be applied to injection molding. However, it was impossible to produce a molded article having stable color tone and physical properties.
In the technical field of the polyimide, a crystalline polyimide for melt molding having not only excellent heat resistance and chemical resistance, which are peculiar to the polyimide, but also high crystallization rate have required. However, such a polyimide has still to be obtained at present.
That is, the problem is that a crystalline polyimide having a repeating unit represented by the chemical formula (1), a molecular terminal being composed of the chemical formula (2) and/or chemical formula (3) is inferior in thermal stability on melting and a melt viscosity ratio MVR calculated by the numerical formula (1) exceeds 1.5.
In the polyimide whose melt viscosity ratio MVR exceeds 1.5, the fluidity is lowered with a lapse of time on melting. Therefore, when the injection molding is conducted, the injection pressure was increased and the fluidity of the resin is lowered with a lapse of time after the beginning of the molding. Accordingly, not only stable molding could not be conducted, but also products having stable color tone and physical properties could not be obtained.
In light of the above problems in the prior art, the present inventors have decided it as an object to be attained by the present invention to provide a crystalline polyimide for melt molding, which has at least excellent characteristics {circle around (1)} to {circle around (4)} described below.
Particularly, it was difficult to realize the characteristics {circle around (1)} described below by the prior art.
{circle around (1)} It is superior in thermal stability on melting. That is, the degree of lowering of the fluidity with a lapse of time on melting is small. It was difficult to realize this feature in the prior art.
{circle around (2)} It has high heat resistance. That is, it has excellent mechanical strength even at the temperature higher than a glass transition temperature (Tg) because of its high crystallizability.
{circle around (3)} It is superior in productivity. That is, since a crystallization rate is large, it is crystallized during a normal short molding cycle without requiring a special heat-treating operation such as operation of slowly cooling in a mold on molding, operation of heat-treating after molding or the like.
{circle around (4)} It is superior in dimensional accuracy. That is, since a crystallization rate is large and it is crystallized in a mold on molding, the degree of shrinkage after molding is small.
To solve the above problems, the present inventors have studied intensively. As a result, they have found that the resulting resin exerts markedly high thermal stability only when using 1,3-bis(4-aminophenoxy)benzene containing no azo compound as a raw material monomer and that stable melt molding can be conducted only when using this resin and the color tone and physical properties of the resulting product are stable. Thus, the present invention has been completed.
That is, a first invention of the present invention relates to a thermoplastic polyimide having good thermal stability, comprising a repeating unit represented by the chemical formula (1), a molecular terminal being composed of the chemical formula (2) and/or chemical formula (3), characterized in that:
a melt viscosity ratio MVR calculated by the numerical formula (1) is within a numerical range shown in the numerical formula (2).
A second invention of the present invention relates to 1,3-bis(4-aminophenoxy)benzene represented by the chemical formula (2), characterized in that the content of an azo compound is from 0.0 to 0.2%, which is used as a raw material of the above polymer.
In the prior art, it was not confirmed that an azo compound as an impurity is present in 1,3-bis(4-aminophenoxy)benzene obtained by a conventional method. Regarding the polyimide obtained by using 1,3-bis(4-aminophenoxy)benzene obtained by a conventional method, the melt viscosity ratio MVR calculated by the numerical formula (1) exceeded 1.5.
It has been bound for the first time by the present inventors that the melt viscosity ratio MVR calculated by the numerical formula (1) of the thermoplastic polyimide is related to the amount of the azo compound in 1,3-bis(4-aminophenoxy)benzene used as the raw material.
The thermoplastic polyimide according to the present invention is characterized in that it is superior in thermal stability on melting and is capable of performing stable melt molding and that the resulting molded article has stable color tone and stable physical properties.
The present invention is specified by the matters described in {circle around (1)} to {circle around (13)} below.
{circle around (1)} A thermoplastic polyimide having good thermal stability, comprising a repeating unit represented by the chemical formula (1), a molecular terminal being composed of the chemical formula (2) and/or chemical formula (3), characterized in that:
a melt viscosity ratio MVR calculated by the numerical formula (1) is within a numerical range shown in the numerical formula (2). 
(in the chemical formula (2), V is a monovalent aromatic group and, in the chemical formula (3), T is a divalent aromatic group)
Numerical Formula 1
MVR=MV30/MV5xe2x80x83xe2x80x83(1)
(in the numerical formula (1), MV5 is a melt viscosity ([Pa.sec]) determined by melting a sample with maintaining at 420xc2x0 C. for 5 minutes and measuring at a shear rate within a range from 30 to 500 [secxe2x88x921], and MV30 is a melt viscosity ([Pa.sec]) determined by melting a sample with maintaining at 420xc2x0 C. for 30 minutes and measuring at a shear rate within a range from 30 to 500 [secxe2x88x921])
Numerical Formula 2
1.0xe2x89xa6MVRxe2x89xa61.5xe2x80x83xe2x80x83(2)
(in the numerical formula (2), MVR is a melt viscosity ratio calculated by the numerical formula (1))
{circle around (2)} A thermoplastic polyimide having good thermal stability, comprising a repeating unit represented by the chemical formula (1), a molecular terminal being composed of the chemical formula (2) and/or chemical formula (3), characterized in that:
a melt index retention MIR calculated by the numerical formula (3) is within a numerical range shown in the numerical formula (4).
Numerical Formula 3
MIR=MI30/MI5xe2x80x83xe2x80x83(3)
(in the numerical formula (3), MI5 is MI ([g/10 min.]) determined by melting a sample with maintaining at 420xc2x0 C. for 5 minutes and measuring under a load of 10.3 N in accordance with ASTM D-1238 and MI30 is MI ([g/10 min.]) determined by melting a sample with maintaining at 420xc2x0 C. for 30 minutes and measuring)
Numerical Formula 4
0.7xe2x89xa6MIRxe2x89xa61.0xe2x80x83xe2x80x83(4)
(in the numerical formula (4), MIR is a melt index retention calculated by the numerical formula (3))
{circle around (3)} 1,3-bis(4-aminophenoxy)benzene represented by the chemical formula (4), characterized in that the content of an azo compound is from 0.0 to 0.2%. 
{circle around (4)} 1,3-bis(4-aminophenoxy)benzene according to {circle around (3)}, wherein the azo compound is at least one selected from the group consisting of compounds represented by the chemical formulas (5) to (7). 
{circle around (5)} 1,3-bis(4-aminophenoxy)benzene according to {circle around (3)} or {circle around (5)}, which is used for production of a thermoplastic polyimide resin having good thermal stability.
{circle around (6)} A method for producing a thermoplastic polyimide having good thermal stability, which comprises using 1,3-bis(4-aminophenoxy)benzene represented by the chemical formula (8), 3,3xe2x80x2,4,4xe2x80x2-biphenyltetracarboxylic anhydride represented by the chemical formula (9), monoamine represented by the chemical formula (10) and/or dicarboxylic anhydride represented by the chemical formula (11), characterized in that:
the content of an azo compound of 1,3-bis(4-aminophneoxy)benzene represented by the chemical formula (8) is from 0.0 to 0.2%. 
(in the chemical formula (10), V is a monovalent aromatic group and, in the chemical formula (11), T is a divalent aromatic group)
{circle around (7)} The method for producing a thermoplastic polyimide having good thermal stability according to {circle around (6)}, wherein the azo compound is at least one selected from the group consisting of compounds represented by the chemical formulas (5) to (7).
{circle around (8)} A thermoplastic polyimide having good thermal stability obtained by the method of {circle around (6)} or {circle around (7)}.
{circle around (9)} A method for producing 1,3-bis(4-aminophenoxy)benzene represented by the chemical formula (13), which comprises previously charging a reaction solvent and a catalyst and then reducing 1,3-bis(4-nitrophenoxy)benzene represented by the chemical formula (12) with gradually adding said 1,3-bis(4-nitrophenoxy)benzene in a reaction vessel in which hydrogen is introduced, characterized in that:
the content of-an azo compound is from 0.0 to 0.2%. 
{circle around (10)} The method for producing a thermoplastic polyimide having good thermal stability according to {circle around (9)}, wherein the azo compound is at least one selected from the group consisting of compounds represented by the chemical formulas (5) to (7).
{circle around (11)} 1,3-bis(4-aminophenoxy)benzene represented by the chemical formula 13 wherein the content of an azo compound is from 0.0 to 0.2%, which is obtained by the method of {circle around (9)} or {circle around (10)}.
{circle around (12)} A molded article comprising a thermoplastic polyimide having a repeating unit represented by the chemical formula (1), a molecular terminal being composed of the chemical formula (2) and/or chemical formula (3), characterized in that:
when the molded article is molten, a melt viscosity ratio MVR calculated by the numerical formula (1) is within a numerical range shown in the numerical formula (2).
Numerical Formula 1
MVR=MV30/MV5xe2x80x83xe2x80x83(1)
(in the numerical formula (1), MV5 is a melt viscosity ([Pa.sec]) determined by melting a sample with maintaining at 420xc2x0 C. for 5 minutes and measuring at a shear rate within a range from 30 to 500 [secxe2x88x921], and MV30 is a melt viscosity ([Pa.sec]) determined by melting a sample with maintaining at 420xc2x0 C. for 30 minutes and measuring at a shear rate within a range from 30 to 500 [secxe2x88x921])
Numerical Formula 2
1.0xe2x89xa6MVRxe2x89xa61.5xe2x80x83xe2x80x83(2)
(in the numerical formula (2), MVR is a melt viscosity ratio calculated by the numerical formula (1))
{circle around (13)} A molded article comprising a thermoplastic polyimide having a repeating unit represented by the chemical formula (1), a molecular terminal being composed of the chemical formula (2) and/or chemical formula (3), characterized in that:
when the molded article is molten, a melt index retention MIR calculated by the numerical formula (3) is within a numerical range shown in the numerical formula (4) [Numerical Formula 4].
Numerical Formula 3
MIR=MI30/MI5xe2x80x83xe2x80x83(3)
(in the numerical formula (3), MI5 is MI ([g/10 min.]) determined by melting a sample with maintaining at 420xc2x0 C. for 5 minutes and measuring under a load of 10.3 N in accordance with ASTM D-1238 and MI30 is MI ([g/10 min.]) determined by melting a sample with maintaining at 420xc2x0 C. for 30 minutes and measuring)
Numerical Formula 4
0.7xe2x89xa6MIRxe2x89xa61.0xe2x80x83xe2x80x83(4)
(in the numerical formula (4), MIR is a melt index retention calculated by the numerical formula (3))